fix(forms): render severity feedback

[Samk13]

❤️ Thank you for your contribution!

Description

• This change keeps curation feedback translated and structured end to end. The backend now guarantees that translated rule text is serialized as strings, while preserving severity metadata.

• The frontend shared error label now understands that structured feedback shape, so generic deposit fields can show warnings and info messages without treating them as plain errors or crashing on object values.

• related: Track i18n work for InvenioRDM v14 invenio-app-rdm#3499

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please reach out to an architect on Discord.

Frontend

• I've followed the CSS/JS and React guidelines.
• I've followed the web accessibility guidelines.
• I've followed the user interface guidelines.

Reminder

By using GitHub, you have already agreed to the GitHub’s Terms of Service including that:

1. You license your contribution under the same terms as the current repository’s license.
2. You agree that you have the right to license your contribution under the current repository’s license.